Inhibitory Action of Troglitazone, an Insulin-Sensitizing Agent, on the Calcium Current in Cardiac Ventricular Cells of Guinea Pig

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We investigated the effects of troglitazone, a new orally active hypoglycemic agent, on the voltage-dependent L-type Ca²⁺ current in single cardiac ventricular myocytes of guinea pigs by the whole-cell voltage clamp technique.Troglitazone blocked the Ca²⁺ currents in a concentration-dependent manner.The inhibitory effect was more potent at the holding potential(HP)of −50mV than at −80mV.The half-maximum inhibiting concentration(IC₅₀)of troglitazone was 0.8μM with the Hill coefficient of 0.84 at −50mV HP.In contrast, the IC₅₀ value was higher than 10μM at −80mV HP.These results suggest that troglitazone at therapeutic concentrations inhibit the Ca²⁺ channels and may exert cardioprotective effects in diabetic conditions.